I used to have down payments of €1000 before work starts on a secured account that neither could access without sufficient proof of reason. If the client broke their contract I would get my insured amount first and they'd only get their refund part (if any), but if I broke my contract I would lose my share, and if the transaction was completed I'd get that down payment plus anything else that I was owed before releasing the final product, or the client would get their refund balance if what I delivered was of a lower bill amount.

Even though software is something different entirely, it's still creative work and that high of a bill filters out anyone not being serious enough about it c: ..great suggestion, and great reminder of those old times too :P